encoding.c: Acquire VM lock around require_silent_safe

`require_silent_safe` calls into `features_index_add` and a few
other routines that need to be synchronized.

There are other Ractor related concerns with autoloaded encodings
but this one is the biggest.

Author: byroot

encoding.c

@@ -725,12 +725,38 @@ rb_enc_get_from_index(int index)
 
 int rb_require_internal_silent(VALUE fname);
 
+static VALUE
+require_silent_safe(VALUE fname)
+{
+    return INT2NUM(rb_require_internal_silent(fname));
+}
+
+static int
+require_silent_sync(VALUE fname)
+{
+    int state;
+    VALUE retval;
+    RB_VM_LOCKING() {
+        VALUE debug = ruby_debug;
+        VALUE errinfo = rb_errinfo();
+
+        ruby_debug = Qfalse;
+
+        retval = rb_protect(require_silent_safe, fname, &state);
+
+        ruby_debug = debug;
+        rb_set_errinfo(errinfo);
+    }
+    if (state) {
+        rb_jump_tag(state);
+    }
+    return NUM2INT(retval);
+}
+
 static int
 load_encoding(const char *name)
 {
     VALUE enclib = rb_sprintf("enc/%s.so", name);
-    VALUE debug = ruby_debug;
-    VALUE errinfo;
     char *s = RSTRING_PTR(enclib) + 4, *e = RSTRING_END(enclib) - 3;
     int loaded;
     int idx;
@@ -741,11 +767,7 @@ load_encoding(const char *name)
         ++s;
     }
     enclib = rb_fstring(enclib);
-    ruby_debug = Qfalse;
-    errinfo = rb_errinfo();
-    loaded = rb_require_internal_silent(enclib);
-    ruby_debug = debug;
-    rb_set_errinfo(errinfo);
+    loaded = require_silent_sync(enclib);
 
     GLOBAL_ENC_TABLE_LOCKING(enc_table) {
         if (loaded < 0 || 1 < loaded) {

load.c

@@ -372,6 +372,8 @@ features_index_add_single(vm_ns_t *vm_ns, const char* str, size_t len, VALUE off
 static void
 features_index_add(vm_ns_t *vm_ns, VALUE feature, VALUE offset)
 {
+    RUBY_ASSERT(rb_ractor_main_p());
+
     const char *feature_str, *feature_end, *ext, *p;
     bool rb = false;
 

test/ruby/test_encoding.rb

@@ -136,4 +136,25 @@ def test_ractor_load_encoding
       assert "[Bug #19562]"
     end;
   end
+
+  def test_ractor_lazy_load_encoding_concurrently
+    assert_ractor("#{<<~"begin;"}\n#{<<~'end;'}")
+    begin;
+      rs = []
+      autoload_encodings = Encoding.list.select { |e| e.inspect.include?("(autoload)") }.freeze
+      7.times do
+        rs << Ractor.new(autoload_encodings) do |encodings|
+          str = "abc".dup
+          encodings.each do |enc|
+            str.force_encoding(enc)
+          end
+        end
+      end
+      while rs.any?
+        r, _obj = Ractor.select(*rs)
+        rs.delete(r)
+      end
+      assert rs.empty?
+    end;
+  end
 end